Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
$$\text{T\_K\_NTA\_EN\_A\_E\_T\_KE\_}$$

Let us count the total number of spaces including blanks. There are $20$ positions. We can divide them into $4$ groups of $5$ letters each or $5$ groups of $4$ letters each.Let's try dividing into groups of $5$:
$$\text{T \_ K \_ N}\mid \text{T A \_ E N}\mid \text{\_ A \_ E \_}\mid \text{T \_ K E \_}$$
By comparing the blocks, we can see a repetitive keyword pattern forming TAKEN / KETAN or similar. Let's analyze carefully:The pattern is a repetition of the 5-letter word TAKEN:$\text{T A K E N}$$\text{T A K E N}$$\text{T A K E N}$$\text{T A K E N}$ Let's gather the inserted blank positions:$\text{A, E, K, T, K, N, A, N}$ This matches exactly option D: AEKTKNAN.